APOE and Alzheimer disease: Like other studies, we also found causal effects of genetic liability to AD on larger thickness in the lateral occipital, which is consistent with two previous studies in healthy individuals where APOE ε4 carriers have a thicker occipital cortex in comparison with normal controls.59 60 The thickening of certain brain regions has been speculated to reflect brain swelling in response to glial activation in preclinical AD stages.61